1. Field of the Invention
The present invention relates to vertical transmission structures, and vertical transmission structures for high-frequency transmission lines.
2. Background of the Related Art
Along with the rapid advances in wireless communication products development in recent years, a planar PCB architecture can not satisfy the demand of low cost, high density and compact products. Thus, the vertical interconnection of low temperature co-fired ceramics (LTCC) package or multi-layer PCB have gradually replaced the design of the planar PCB. However, the via design for the multi-layer PCB or LTTC may cause parasitic impedances or inductances.
There have been various types for vertical transmission, such as transmission between microstrip line and strip line, microstrips, coplanar waveguides, or coplanar waveguide and strip line. Taking the first type as an example, the vertical transmission interconnects between the coplanar waveguides do not cause large return loss in low frequencies, however, the parasitic effects from the vertical transmission interconnects can degrade the characteristics of return parameters with increase in the operating frequencies. Generally, the compensation of local matching may reduce the parasitic effects and further convert them to an inductance effect to achieve both the impedance match and prevent the parasitic effects. In the second type, the microstrip line transmission with slots or cavities does not adopt a via architecture to prevent the parasitic effects. The slot configuration may generate inductance effects to achieve impedance match. The improved cavity configuration includes both a dielectric layer between two ground layers made of a same metallic material and a slot to perform coupling by waveguides. In the third type, the transmission between microstrip line and strip line improves frequency band characteristics by high impedance compensation that utilizes a high-impedance line with additional inductance to compensate the capacitance of transmission lines. It may be due to different impedances generated by the lines with various widths. The impedances may be raised by decreasing the widths and converted into inductances.
FIG. 1 is a top-view perspective diagram illustrating a conventional three ground bump configuration of a high-frequency flip chip package. A substrate 10 has a coplanar waveguide 12. The circuit layer 16 of a microwave chip package 18 is coupled to the coplanar waveguide 12 via three bumps 14. There are various transmission structures applied to various packages. Basically, the parasitic effects from various wiring configurations of the packages are raised with increase of operating frequencies. Thus, flip chip package has been gradually applied to high-frequency products. However, when the underfill comes in contact with the transmission structures of the flip chip package, significant waveband frequency loss of transmission lines occurs. Attempts are still being made to improve the transmission architecture of transmission lines to achieve reduction in the loss of waveband frequency.